As curing agents for epoxy resins, amine-containing compounds, carboxylic anhydride and mercapto compounds, all of which are being widely used for two-part system, have been known. In two-part system, however, it is necessary to mix each components in absolutely uniform, and time for several hours are required for resulting the curing.
In addition, there is another problem in the curing in two-part system such as difficulty in the production because of its short pot life as long as from several hours to several days due to consecutive continuance of curing reaction proceeding even at room temperature.
Whereas, boron fluoride and monoethyl amine combination have been known as an agent for curing epoxy resins in one-part system. However, there are problems in the curing such that temperature required for the curing is very high as much as 160.degree. C. and time duration of from 1 to 8 hours is required for the completion of the curing.
Aiming at solving such problems described above, pyridinium salt compounds are disclosed in JP Laid-Opened No. Hei 1-299270. By using pyridinium salt compounds. The execution of curing in one-part system and shortening of time required for the curing could have been realized, however, another problem of high temperature required for the curing has not been improved.
Further to said pyridinium salt compounds, the following sulfonium salt compounds similar to the compounds specified in the present invention have been disclosed. ##STR2##
However, sulfonium salt compounds disclosed in both JP Laid-Opened No. 2-178319 and JP Patent Examined Gazette No. Sho 63-12092 are still requiring high temperature to complete curing, and therefore, it is difficult to obtain cured-products having good physical property when using epoxy resins being widely used, such as bisphenol A diglycidyl ether.
Besides, sulfonium salt compounds described in JP Patent Examined Gazette No. Sho 63-12092 are mostly prepared from sulfide compounds having low boiling point, and therefore, the sulfonium salt compound itself and the cured-product thereof give bad smell in most cases.
On the other hand, sulfonium salt compounds described in JP Laid-Opened No. Hei 2-196812 are prepared from aromatic sulfide compounds in solid, and therefore, those sulfonium salt compounds do not give bad smell. However, because of their physical state in solid, said sulfonium salt compounds have a problem in the solubility in monomer. In addition, physical properties of the cured-products therewith tend to be no good. Furthermore, it is not easy to use sulfonium salt compounds capable of curing resins at less than 150.degree. C. in one-part system.